Waste heat source transcritical CO2 heat pump system and optimization method thereof

Abstract

The invention discloses a waste heat source transcritical CO2 heat pump system and an optimization method thereof. The waste heat source transcritical CO2 heat pump system comprises a refrigerant connecting pipeline, a gas cooler water side connecting pipeline, an evaporator water side connecting pipeline and a PID control module connected with the refrigerant connecting pipeline, the gas cooler water side connecting pipeline and the evaporator water side connecting pipeline. The compressor is connected with a first gas cooler, the first gas cooler is connected with an intermediate heat regenerator, the intermediate heat regenerator is connected with a second gas cooler, the second gas cooler is connected with an electronic expansion valve, the electronic expansion valve is connected with an evaporator, the evaporator is connected with the intermediate heat regenerator, the intermediate heat regenerator is connected with the compressor, and the intermediate heat regenerator is connected with a bypass adjusting valve in parallel. A water inlet of the second gas cooler is provided with a first water pump, a water outlet of the second gas cooler is connected with a water inlet of the first gas cooler, and the water side of the second gas cooler is connected with a water temperature adjusting valve in parallel. A second water pump is arranged at a water inlet of the evaporator. Under the conditions of a waste heat source and a low pressure ratio, deep utilization of waste heat resources can be achieved, and intermediate temperature backheating required by high heat supply temperature is met.

Description

Technical Field

[0001] The present invention belongs to the technical fields of thermodynamics and heat pump technology, and in particular relates to a waste heat source transcritical CO 2 heat pump system and its optimization method. Background Art

[0002] In industries such as iron and steel, construction, and metallurgy, industrial waste heat is seriously wasted. Approximately 70% of the waste heat is discharged in the form of hot flue gas and wastewater, and the current recovery and utilization rate is only 30%. Therefore, there is still great potential for improving waste heat utilization. In addition, many industrial fields have a high demand for hot water at 80 - 100°C. However, the existing heating methods (such as direct heat exchange, electric heating, and primary energy combustion) have low energy efficiency and high pollution, resulting in a large amount of energy waste and increasing energy consumption and environmental pollution. The waste heat source CO 2 heat pump, as an advanced heating technology, has excellent heating performance. By recovering the neglected waste heat, the electrothermal conversion efficiency can exceed 350%, and even reach more than 400% under suitable working conditions. It not only reduces energy consumption and costs, but also reduces the dependence on traditional energy, lightens the environmental burden, and provides a more environmentally friendly and efficient solution for industrial high-temperature heating.

[0003] Currently, most of the industrial heat pumps in use are air-source transcritical CO 2 heat pumps, whose advantage is that they can meet the high-temperature heating demand in low-temperature environments. Compared with air-source heat pumps, the evaporation temperature of the waste heat source transcritical CO 2 heat pump is usually higher, and the increase space of its discharge pressure is limited. Therefore, the compression ratio of the waste heat source CO 2 heat pump is generally smaller than that of the air-source CO 2 heat pump. Therefore, the previous cycle technology of compressor - gas cooler - regenerator - throttle valve - evaporator will be ineffective and difficult to meet the heating demand of 80 - 100°C under the premise of ensuring the rationalization of the performance index and the simplification of technology.

[0004] However, there is currently little research on intermediate temperature regeneration, especially the research on the control strategy and optimization method of the waste heat source transcritical CO 2 heat pump system is relatively imperfect. In the design and optimization process of the waste heat source transcritical CO 2 heat pump system, the increase in discharge pressure usually leads to an increase in discharge temperature, which can, to a certain extent, improve the system's heat recovery efficiency and increase the heating capacity. However, the increase in discharge pressure may also lead to an increase in the compressor load, thereby causing an increase in system power consumption and resulting in adverse consequences such as excessive regulation causing too high compressor temperature or system overload. Summary of the Invention

[0005] The purpose of the present invention is to provide a waste heat source transcritical CO2 Heat pump system and its optimization method, which solve the problem that the existing transcritical CO 2 heat pump technology cannot supply high-temperature heat under the conditions of waste heat source and low pressure ratio.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions: A waste heat source transcritical CO 2 heat pump system, including a refrigerant connection pipeline, a water side connection pipeline of a gas cooler, a water side connection pipeline of an evaporator, and a PID control module; A compressor is arranged in the refrigerant connection pipeline. The outlet of the compressor is connected to the inlet of a first gas cooler. The outlet of the first gas cooler is connected to the high-pressure side inlet of an intermediate heat exchanger. The high-pressure side outlet of the intermediate heat exchanger is connected to the inlet of a second gas cooler. The outlet of the second gas cooler is connected to an electronic expansion valve. The electronic expansion valve is connected to the inlet of the evaporator. The outlet of the evaporator is connected to the low-pressure side inlet of the intermediate heat exchanger. The low-pressure side outlet of the intermediate heat exchanger is connected to the inlet of the compressor. A bypass regulating valve is connected in parallel to the high-pressure side of the intermediate heat exchanger; In the water side connection pipeline of the gas cooler, a first water pump is arranged at the water inlet of the second gas cooler. The water outlet of the second gas cooler is connected to the water inlet of the first gas cooler. The water outlet of the first gas cooler is connected to a high-temperature hot water usage place. A water temperature regulating valve is connected in parallel to the water side of the second gas cooler; In the water side connection pipeline of the evaporator, a second water pump is arranged at the water inlet of the evaporator. The water outlet of the evaporator is connected to a low-temperature waste water storage place; The electronic expansion valve, the bypass regulating valve, the water temperature regulating valve, the first water pump, and the second water pump are all connected to the PID control module.

[0007] Furthermore, a first temperature sensor and a pressure sensor are arranged on the outlet pipeline of the compressor.

[0008] Furthermore, a fifth temperature sensor is arranged on the outlet pipeline of the first gas cooler, a second temperature sensor is arranged on the inlet pipeline of the first gas cooler, and a third temperature sensor is arranged on the outlet pipeline of the first gas cooler.

[0009] Furthermore, a sixth temperature sensor and a second solenoid valve are arranged on the pipeline between the water inlet of the second gas cooler and the first water pump.

[0010] Furthermore, a flow meter is installed on the parallel pipeline of the water side of the second gas cooler.

[0011] Furthermore, a gas-liquid separator is connected between the outlet of the evaporator and the low-pressure side inlet of the intermediate heat exchanger.

[0012] Further, a seventh temperature sensor and a first solenoid valve are provided on the pipeline between the water inlet of the evaporator and the second water pump, and a fourth temperature sensor is provided on the water outlet pipeline of the evaporator.

[0013] Further, the PID control module includes a compressor discharge pressure PID controller, a compressor discharge temperature PID controller, a water-side intermediate temperature PID controller, a high-temperature hot water output temperature PID controller, and a low-temperature waste water output temperature PID controller. The compressor discharge pressure PID controller is connected to the electronic expansion valve, the compressor discharge temperature PID controller is connected to the bypass regulating valve, the water-side intermediate temperature PID controller is connected to the water temperature regulating valve, the high-temperature hot water output temperature PID controller is connected to the first water pump, and the low-temperature waste water output temperature PID controller is connected to the second water pump.

[0014] An optimization method for a waste heat source transcritical CO 2 heat pump system, comprising: waste heat source transcritical CO 2 When the waste heat source transcritical CO heat pump system operates, the opening degree of the electronic expansion valve is adjusted through the PID control module to make the discharge pressure of the compressor reach the optimal value; the opening degree of the bypass regulating valve is adjusted through the PID control module to make the discharge temperature of the compressor and the heat recovery rate of the intermediate heat exchanger reach the optimal value; the opening degree of the water temperature regulating valve is adjusted through the PID control module to make the water-side intermediate temperature reach the set value; the rotation speed of the first water pump is adjusted through the PID control module to make the high-temperature hot water output temperature reach the set value; the rotation speed of the second water pump is adjusted through the PID control module to make the low-temperature waste water output temperature reach the set value.

[0015] Further, the optimization process of the discharge pressure of the compressor is as follows: the compressor discharge pressure PID controller adjusts the refrigerant flow rate of the control system by adjusting the opening degree of the electronic expansion valve according to the set value and the actual value of the compressor discharge pressure, so that the discharge pressure of the compressor reaches the optimal value; The optimization process of the discharge temperature of the compressor and the heat recovery rate of the system is as follows: the compressor discharge temperature PID controller adjusts the refrigerant flow rate of the intermediate heat exchanger by adjusting the opening degree of the bypass regulating valve according to the set value and the actual value of the compressor discharge temperature, so that the discharge temperature of the compressor and the heat recovery rate of the intermediate heat exchanger reach the optimal value; The optimization process of the water-side intermediate temperature is as follows: the water-side intermediate temperature PID controller adjusts the opening degree of the water temperature regulating valve according to the water-side intermediate temperature and the refrigerant-side intermediate temperature of the first gas cooler and the second gas cooler, changes the water-side intermediate temperature value, so that the water-side intermediate temperatures of the first gas cooler and the second gas cooler reach the set value; The optimization process of the high-temperature hot water output temperature is as follows: The high-temperature hot water output temperature PID controller adjusts the rotational speed of the first water pump according to the set value of the high-temperature hot water output temperature and the actual value of the water temperature at the outlet of the first gas cooler, changes the flow rate of the cooling water makeup, and makes the water temperature at the outlet of the first gas cooler reach the set value. The optimization process of the low-temperature wastewater output temperature is as follows: The low-temperature wastewater output temperature PID controller adjusts the rotational speed of the second water pump according to the set value of the outlet water temperature after heat exchange of the waste heat waste hot water and the actual value of the water temperature at the outlet of the evaporator, changes the flow rate of the surplus hot water makeup on the water side of the evaporator, and makes the water temperature at the outlet of the evaporator reach the set value.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a waste heat source transcritical CO 2 heat pump system. By connecting the refrigerant connection pipeline, the water side connection pipeline of the gas cooler, the water side connection pipeline of the evaporator to the PID control module. In the refrigerant connection pipeline, the compressor is connected to the first gas cooler, the first gas cooler is connected to the intermediate heat exchanger, the intermediate heat exchanger is connected to the second gas cooler, the second gas cooler is connected to the electronic expansion valve, the electronic expansion valve is connected to the evaporator, the evaporator is connected to the intermediate heat exchanger, and the intermediate heat exchanger is connected to the compressor. The intermediate heat exchanger is arranged between the first gas cooler and the second gas cooler, so that the high-pressure refrigerant entering the intermediate heat exchanger has a relatively high temperature. On the premise of ensuring that the performance of other state parameter points of the system changes little, the heat recovery amount of the intermediate heat exchanger is increased, the suction temperature of the compressor is increased, and thus the discharge temperature is increased, solving the problem of the waste heat source transcritical CO 2The problem of low compressor exhaust temperature caused by low compression ratio in the heat pump. A bypass regulating valve is connected in parallel on the high-pressure side of the intermediate regenerator, and the heat regeneration rate of the intermediate regenerator is dynamically adjusted through a certain control algorithm, so that on the premise that the exhaust pressure is the optimal value, the exhaust temperature of the system is adjusted at the same time to achieve the optimum, realize more refined system control, and ensure the efficient operation and stability of the system. In the connecting pipeline on the water side of the gas cooler, a first water pump is arranged at the water inlet of the second gas cooler, the water outlet of the second gas cooler is connected to the water inlet of the first gas cooler, and a water temperature regulating valve is connected in parallel on the water side of the second gas cooler; in the connecting pipeline on the water side of the evaporator, a second water pump is arranged at the water inlet of the evaporator. Water pump devices are arranged at the water inlets of the first gas cooler and the evaporator on the water side. By adjusting the flow rates of the water circuits of the gas cooler and the evaporator through the PID control algorithm of the outlet water temperature, the outlet water temperature of the gas cooler side and the outlet water temperature of the evaporator side can be effectively controlled to be stable at the set ideal values. The structure of the present invention is simple, and the performance index is rationalized. By adopting intermediate temperature regeneration of the two-stage gas cooler, it can adapt to the low pressure ratio and variable working conditions when using surplus hot water as the heat source, and can meet the high-temperature water supply temperature requirement of more than 95 °C under the condition of low pressure ratio. The PID control module realizes the adaptive adjustment of the compressor exhaust temperature and the exhaust pressure by adjusting the rotational speed of the compressor, the opening degree of the control valve, etc. according to the system requirements and the surplus hot water temperature conditions, effectively optimizes the transcritical CO of the surplus heat source 2 The heating coefficient of the heat pump system, improves the heat regeneration efficiency, reduces the energy consumption, and ensures the efficient and stable operation of the system under variable working conditions. It meets the intermediate temperature regeneration of the system under the conditions of surplus heat source and low pressure ratio, which can realize the deep utilization of the surplus heat resource and meet the high heating temperature requirement.

[0017] Furthermore, the first gas cooler, the second gas cooler, the intermediate regenerator and the evaporator all adopt the reverse cross-pipe arrangement method to improve the heat exchange efficiency. This cross-pipe design not only enhances the heat exchange efficiency, but also flexibly supports the switching between various operating conditions, has strong adaptability, and ensures the stability and energy saving of the system operation.

[0018] Furthermore, the PID control module of the present invention adopts an advanced PID controller, which has the ability of rapid response, and calculates through the difference method. Combining the boundary conditions of the working conditions of the real-time monitoring system, it can be quickly adjusted under different working conditions to achieve a rapid response to the system and maintain the efficient operation of the system.

[0019] The present invention also provides a transcritical CO of surplus heat source 2 Optimization method of heat pump system. Under the conditions of surplus heat source and low pressure ratio, the transcritical CO of surplus heat source 2According to the system requirements and the boundary conditions of the water circuits on the evaporator and gas cooler sides, the heat pump system changes the exhaust pressure, exhaust temperature, and heat regeneration rate of the system to approach the optimal values by precisely adjusting the opening degrees of the electronic expansion valve and the bypass regulating valve, enabling the system to reach the best operating state. This ensures that the system has optimal performance in various working parameter regions, effectively improves the energy efficiency of the system, ensures stable operation under different loads and working conditions, and realizes the use of waste heat sources for transcritical CO 2 Coupled optimization of the heat pump exhaust pressure and exhaust temperature. Secondly, the intermediate temperature of the water circuit on the gas cooler side is flexibly adjusted to optimize the thermal efficiency and stability of the system, enabling transcritical CO to be achieved under different loads and external conditions 2 High-efficiency operation and energy-saving effect of the heat pump system. With the PID control logic algorithm, according to the real-time working state of the system and the boundary conditions of system operation, the control parameters of the system are dynamically adjusted in a timely manner to achieve precise control of the system and optimize the system performance to the greatest extent. The present invention can replace traditional methods such as electric heating and primary energy combustion heating in industrial heating below 100°C, flexibly utilize medium- and low-temperature waste heat energy, provide heating hot water below 100°C with an electro-thermal conversion efficiency exceeding 350%, and is expected to bring sustainable, efficient, and economical heating solutions to the industrial field Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings

[0021] Figure 1 For the transcritical CO of the waste heat source of the present invention 2 Structural schematic diagram of the heat pump system

[0022] Figure 2 For the transcritical CO of the waste heat source of the present invention 2 Schematic diagram of the control module of the heat pump system

[0023] Figure 3 For the transcritical CO of the waste heat source of the present invention 2 Flowchart of the optimization method for the heat pump system

[0024] Wherein: 1 - compressor, 2 - first gas cooler, 3 - second gas cooler, 4 - intermediate regenerator, 5 - electronic expansion valve, 6 - evaporator, 7 - gas-liquid separator, 8 - bypass regulating valve, 9 - water temperature regulating valve, 10 - flowmeter, 11 - first water pump, 12 - second water pump, 13 - first solenoid valve, 14 - second solenoid valve, 15 - first temperature sensor, 16 - pressure sensor, 17 - second temperature sensor, 18 - third temperature sensor, 19 - fourth temperature sensor, 20 - fifth temperature sensor, 21 - sixth temperature sensor, 22 - seventh temperature sensor. Detailed implementation manners

[0025] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention generally described and illustrated in the accompanying drawings herein can be arranged and designed in a variety of different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but is merely representative of selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0027] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not require further definition and explanation in subsequent drawings.

[0028] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship in which the product of the invention is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, terms such as "first" and "second" are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0029] In addition, if the term "horizontal" is used, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0030] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if the terms "set", "installed", "connected", and "coupled" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings: See Figure 1 , the present invention provides a waste heat source transcritical CO 2 heat pump system, including a refrigerant connection pipeline, a water side connection pipeline of a gas cooler, a water side connection pipeline of an evaporator, and a PID control module.

[0032] In the refrigerant connection pipeline, the refrigerant outlet of the compressor 1 is connected to the refrigerant inlet of the first gas cooler 2. The refrigerant outlet of the first gas cooler 2 is divided into two paths. One path is connected to the high-pressure side refrigerant inlet of the intermediate regenerator 4, and the other path is connected to the refrigerant inlet of the bypass regulating valve 8. The high-pressure side refrigerant outlet of the intermediate regenerator 4 and the refrigerant discharged from the bypass regulating valve 8 are mixed and then enter the refrigerant inlet of the second gas cooler 3. The refrigerant outlet of the second gas cooler 3 is connected to the refrigerant inlet of the electronic expansion valve 5. The refrigerant outlet of the electronic expansion valve 5 is connected to the refrigerant inlet of the evaporator 6. The refrigerant outlet of the evaporator 6 is connected to the refrigerant inlet of the gas-liquid separator 7. The refrigerant outlet of the gas-liquid separator 7 is connected to the low-pressure side refrigerant inlet of the intermediate regenerator 4. The low-pressure side refrigerant outlet of the intermediate regenerator 4 is connected to the refrigerant inlet of the compressor 1.

[0033] A first temperature sensor 15 and a pressure sensor 16 are provided on the outlet pipeline of the compressor 1 to detect the temperature and pressure of the CO 2 working medium at the exhaust state point of the compressor 1. A fifth temperature sensor 20 is provided on the outlet pipeline of the first gas cooler 2 to detect the refrigerant outlet temperature of the first gas cooler 2, that is, the intermediate temperature on the refrigerant side.

[0034] In the water-side connecting pipeline of the gas cooler, the cooling water make-up water is introduced into the first water pump 11. The water outlet of the first water pump 11 is divided into two paths. One path is connected to the water inlet of the second gas cooler 3, and the other path is connected to the water inlet of the flow meter 10. The water outlet of the flow meter 10 is communicated with the water inlet of the water temperature regulating valve 9. The water outlet of the water temperature regulating valve 9 and the water outlet of the second gas cooler 3 are merged and then introduced into the first gas cooler 2. The water temperature regulating valve 9 is used to control that the intermediate temperature value on the water side will not be too large to cause the exhaust temperature to exceed the normal range, and plays a role in protecting the normal operation of the compressor 1 without failure. The water flowing out of the first gas cooler 2 flows to the industrial site using high-temperature hot water. A second temperature sensor 17 is provided on the pipeline where the water outlet of the water temperature regulating valve 9 and the water outlet of the second gas cooler 3 are merged and lead to the first gas cooler 2, which is used to detect the temperature of the water at the water inlet state point of the first gas cooler 2, that is, the intermediate temperature on the water side. A third temperature sensor 18 is provided on the water outlet pipeline of the first gas cooler 2, which is used to detect the temperature of the water at the water outlet state point of the first gas cooler 2. A second solenoid valve 14 and a sixth temperature sensor 21 are installed on the pipeline from the water outlet of the first water pump 11 to the pipeline before the flow is not divided. The sixth temperature sensor 21 is used to detect the temperature of the cooling water make-up water.

[0035] In the water-side connecting pipeline of the evaporator, the waste heat wastewater make-up water is introduced into the second water pump 12. The water outlet of the second water pump 12 is connected to the water inlet of the evaporator 6. The water outlet of the evaporator 6 leads to the low-temperature wastewater storage. A first solenoid valve 13 and a seventh temperature sensor 22 are installed on the pipeline between the water outlet of the second water pump 12 and the water inlet of the evaporator 6. The seventh temperature sensor 22 is used to detect the temperature of the waste heat wastewater make-up water. A fourth temperature sensor 19 is provided on the water outlet pipeline of the evaporator 6, which is used to detect the temperature of the water at the water outlet state point of the evaporator 6.

[0036] As Figure 2 shown, the PID control module includes a compressor discharge pressure PID controller, a compressor discharge temperature PID controller, a water-side intermediate temperature PID controller, a high-temperature hot water output temperature PID controller, and a low-temperature wastewater output temperature PID controller. The compressor discharge pressure PID controller is connected to the electronic expansion valve 5, the compressor discharge temperature PID controller is connected to the bypass regulating valve 8, the water-side intermediate temperature PID controller is connected to the water temperature regulating valve 9, the high-temperature hot water output temperature PID controller is connected to the first water pump 11, and the low-temperature wastewater output temperature PID controller is connected to the second water pump 12.

[0037] The present invention also provides an optimization method for a waste heat source transcritical CO 2 heat pump system, which ensures that the system can maintain the best performance under different operating conditions through feedback control and intelligent adjustment strategies based on the PID controller. As Figure 3 shown, it specifically includes: waste heat source transcritical CO 2When the heat pump is operating, the opening degree of the electronic expansion valve 5 is adjusted through the compressor discharge pressure PID controller to make the discharge pressure of the compressor 1 reach the optimal value; the opening degree of the bypass regulating valve 8 is adjusted through the compressor discharge temperature PID controller to make the discharge temperature of the compressor 1 and the heat recovery rate of the intermediate heat exchanger 4 reach the optimal value; the rotational speed of the first water pump 11 is adjusted through the high-temperature hot water output temperature PID controller to make the water temperature at the outlet of the first gas cooler 2 reach the set value; the rotational speed of the second water pump 12 is adjusted through the low-temperature waste water output temperature PID controller to make the water temperature at the outlet of the evaporator 6 reach the set required value; the opening degree of the water temperature regulating valve 9 is adjusted through the water-side intermediate temperature PID controller to make the water-side intermediate temperature of the first gas cooler 2 and the second gas cooler 3 reach the set value.

[0038] Adaptive adjustment of the discharge temperature and the system heat recovery rate: The definition formula of the heat recovery rate (Rh) is the ratio of the actual recovered heat quantity of the current heat exchanger in the system operation to the maximum heat recovery quantity of the heat exchanger. A bypass regulating valve 8 is arranged in parallel on the high-pressure side of the intermediate heat exchanger 4. Therefore, there is an optimal heat recovery rate (R h,opt ) during the system operation. The optimal heat recovery rate of the system operation changes with the change of the operating conditions. By adjusting the opening degree of the bypass regulating valve 8, the refrigerant flow rate of the intermediate heat exchanger 4 is controlled, so as to adjust the heat recovery rate of the intermediate heat exchanger 4 and the discharge temperature of the compressor 1. The maximum heat recovery quantity of the intermediate heat exchanger 4 is the heat exchange quantity of the intermediate heat exchanger 4 under the operating conditions when the bypass regulating valve 8 is completely closed. Specifically, the heat recovery rate is related to the make-up water temperature of the surplus hot water (T 22 ), the discharge temperature (T 15 ), the make-up water temperature of the cooling water (T 21 ), the intermediate temperature on the refrigerant side (T 20 ), etc. With the sole purpose of adjusting and controlling the discharge temperature and the heat recovery rate to the optimal values and making the system coefficient of performance (COP) the best, an association model between the heat recovery rate and these variables is constructed, and the association formula is:

[0039] Adjust T 22 , T 15 , T 21 , T 20 parameters according to different modes. With the opening degree of the bypass regulating valve 8 as the input variable, the compressor discharge temperature PID controller outputs the set value of the discharge temperature T 15 . According to the real-time feedback of the parameters of each state point of the system, the numerical values of T 18 and T 19 , the three parameters of the compressor discharge temperature PID controller are adjusted online , and After the system goes through a cycle, if the difference between the set value and the actual value of the exhaust gas temperature before and after the cycle is greater than the set precision value, the difference between the two is used as an input parameter and input into the compressor exhaust gas temperature PID controller. The compressor exhaust gas temperature PID controller calculates the control quantity based on the error of the input parameter, adjusts the exhaust gas temperature of compressor 1, and adjusts the heat regeneration rate in real time to optimize the system performance.

[0040] The compressor exhaust gas temperature PID controller uses the difference method for calculation, and the bypass regulating valve 8 dynamically adjusts the opening degree The calculation formula is:

[0041] Where is the difference between the actual exhaust gas temperature and the set exhaust gas temperature, n is the number of operations, , and are the proportional regulation coefficient, integral regulation coefficient, and differential regulation coefficient respectively. Based on the current operating conditions, according to the heat regeneration rate correlation formula, the optimal heat regeneration rate of the surplus heat water source transcritical CO 2 heat pump is R h，opt , and the corresponding optimal exhaust gas temperature is T 15，opt . Set the proportional regulation parameter, integral regulation parameter, and differential regulation parameter to take values , , .

[0042] Adaptive regulation of the exhaust pressure: When the system is running, since the expansion valve in the system of the present invention is an electronic expansion valve, there is an optimal exhaust pressure (P 16,opt ) during the operation of the system. The optimal exhaust pressure is the exhaust pressure corresponding to the maximum heating coefficient (COP) that the transcritical CO 2 heat pump system can reach. After heating the intermediate regenerator 4 in the transcritical CO 2 heat pump system, the dryness and superheat have little effect on the system exhaust pressure. The optimal exhaust pressure of the system operation changes with the change of the operating conditions. The exhaust pressure mainly depends on the CO 2 working fluid phase state (X), surplus heat water makeup temperature (T 22 ), cooling water makeup temperature (T 21 ), evaporation temperature, condensation temperature, outlet water temperature of the water circuits on the evaporator and gas cooler sides, etc. With the goal of adjusting and controlling the exhaust pressure of compressor 1 to the optimal value and improving the heating coefficient of the heat pump system, an association model between the exhaust pressure and these variables is established. The correlation formula is:

[0043] Taking the opening degree of the electronic expansion valve 5 as the input variable, the compressor discharge pressure PID controller outputs the set value of the discharge pressure, and adjusts the three parameters of the compressor discharge pressure PID controller according to the system dynamic characteristics. , and . Based on the control loop of the waste heat source transcritical CO 2 heat pump model, determine the steady-state limit, adjust the value to make the system have a steady-state oscillation. After the system goes through a cycle, if the deviation between the set value and the actual value of the discharge pressure before and after the cycle is greater than the set accuracy value, then the difference between the two is used as the input parameter and input into the compressor discharge pressure PID controller. The compressor discharge pressure PID controller calculates the control quantity according to the error of the input parameter and adjusts the discharge pressure at the compressor outlet. As the parameter settings of the compressor discharge pressure PID controller are reasonable, the calculated discharge pressure will get closer and closer to the assumed target value until the absolute value of the difference between the two is less than the set accuracy value. According to different working conditions, adjust multiple parameters to adjust the discharge pressure in real time with the compressor discharge pressure PID controller to make the system performance reach the best.

[0044] The compressor discharge pressure PID controller is calculated by the difference method, and the electronic expansion valve 5 dynamically adjusts the opening degree The calculation formula is:

[0045] Where is the difference between the actual discharge pressure and the set discharge pressure, n is the number of operations, , and are the proportional adjustment coefficient, integral adjustment coefficient and differential adjustment coefficient respectively. Taking the current operating condition as the condition, calculate the optimal discharge pressure P 2 of the waste heat water source transcritical CO 16，opt heat pump according to the discharge pressure correlation formula, and set the proportional adjustment parameter, integral adjustment parameter and differential adjustment parameter to take values , , .

[0046] Adaptive adjustment of the intermediate temperature: There is a maximum value and a minimum value for the intermediate temperature. The maximum value is when the water temperature regulating valve 9 is completely closed and all the water flow passes through the second gas cooler 3, and the water-side intermediate temperature at this time is the maximum temperature; the minimum value is when the water temperature regulating valve 9 is completely open and all the water flow passes through one side of the water temperature regulating valve 9, and the second gas cooler 3 does not work, and the water-side intermediate temperature at this time is the minimum temperature. There is an optimal intermediate temperature (T 17,opt), and the optimal intermediate temperature on the water side of the system changes with the operating conditions. There is a positive linear correlation between the intermediate temperature on the water side and the intermediate temperature on the refrigerant side. An increase in the intermediate temperature on the water side will cause the intermediate temperature on the refrigerant side to increase as well. Therefore, only the intermediate temperature on the water side needs to be controlled. After testing, the optimal intermediate temperature in this system is the maximum intermediate temperature, that is, when the water temperature regulating valve 9 is fully closed, the intermediate temperature is the highest and the system performance is the best. However, if the intermediate temperature is too high, the heat transfer amount of the intermediate regenerator 4 increases, causing the suction temperature of the compressor 1 to increase as well, which may pose a risk of too high exhaust temperature of the compressor 1. To avoid this situation, the water temperature regulating valve 9 is specifically set. Therefore, the optimal intermediate temperature is the intermediate temperature corresponding to the maximum heating coefficient of the system under the premise of ensuring the safe operation of the system equipment. Specifically, the intermediate temperature on the water side is related to the exhaust pressure (P 16 ) of the compressor, the exhaust temperature (T 15 ), the makeup water temperature of the cooling water (T 21 ), the output temperature of the high-temperature hot water (T 18 ), and other factors. With the aim of adjusting and controlling the intermediate temperature on the water side to the optimal value under the condition of safe exhaust temperature and improving the heating coefficient of the heat pump system, an association model between the intermediate temperature on the water side and these variables is established. The association formula is:

[0047] Taking the opening of the water temperature regulating valve 9 as the input variable, the water side intermediate temperature PID controller outputs the set value of the water side intermediate temperature. According to the real-time feedback of the system and the exhaust temperature T 15 , the three parameters , and of the water side intermediate temperature PID controller are dynamically adjusted. After one cycle of the system, if the difference in the water side intermediate temperature before and after the cycle is greater than the set accuracy value, the difference between the two is used as the input parameter and input into the water side intermediate temperature PID controller. The water side intermediate temperature PID controller calculates the control amount according to the error of the input parameter, adjusts the opening of the water temperature regulating valve 9, and changes the water side intermediate temperature value so that the actual temperature T 15 can be stabilized within a safe range; The water side intermediate temperature PID controller uses the difference method for calculation, and the calculation formula for the dynamic adjustment of the opening of the water temperature regulating valve 9 is;

[0048] Among them, is the difference between the actual exhaust temperature and the set exhaust temperature, n is the number of operations, , and They are the proportional adjustment coefficient, the integral adjustment coefficient, and the differential adjustment coefficient respectively. Based on the current operating conditions, the surplus heat source transcritical CO 2 The maximum water-side intermediate temperature of the heat pump is T 17，max , if the corresponding exhaust gas temperature T 15 does not exceed the exhaust gas temperature safety range, then the maximum water-side intermediate temperature T 17，max is the optimal water-side intermediate temperature T 17，opt , if the corresponding exhaust gas temperature T 15 exceeds the exhaust gas temperature safety range, then a reasonable maximum exhaust gas temperature T 15，max needs to be recalculated through the water-side intermediate temperature correlation formula, and the water-side intermediate temperature value corresponding to it is the optimal water-side intermediate temperature T 17，opt under the working conditions. According to the optimal water-side intermediate temperature T 17，opt calculated under specific working conditions, set the proportional adjustment parameter, the integral adjustment parameter, and the differential adjustment parameter to take values , , .

[0049] Adaptive adjustment of the high-temperature hot water output temperature: The high-temperature hot water output temperature (T 18 ) is related to the cooling water makeup temperature (T 21 ), the exhaust pressure (P 16 ), the cooling water makeup flow rate (F 11 ), as well as the condensation temperature, the refrigerant phase state, etc. Taking the adjustment of the high-temperature hot water output temperature of the heat pump system to the set temperature as the only goal, an association model between the high-temperature hot water output temperature and these variables is established, and the association formula is:

[0050] Taking the rotational speed of the first water pump 11 as the input variable, the high-temperature hot water output temperature PID controller outputs the set value of the high-temperature hot water output temperature, and adjusts the three parameters , and of the high-temperature hot water output temperature PID controller according to the system dynamic characteristics. After the system goes through one cycle, if there is a difference in the high-temperature hot water output temperature before and after the cycle, then the difference between the two is used as the input parameter and input into the high-temperature hot water output temperature PID controller. The high-temperature hot water output temperature PID controller calculates the control amount according to the error of the input parameter, adjusts the rotational speed of the first water pump 11, and changes the flow rate of the cooling water makeup. As the parameters of the high-temperature hot water output temperature PID controller are set reasonably, the calculated result temperature will get closer and closer to the assumed target value until the difference between the two is 0; adjust multiple parameters according to different working conditions, and supplement the real-time adjustment of the high-temperature hot water output temperature by the high-temperature hot water output temperature PID controller to make the hot water output by the system reach the set demand value; The high-temperature hot water output temperature PID controller calculates by the difference method, and the first water pump 11 dynamically adjusts the rotation speed The calculation formula is:

[0051] Among them, is the difference between the set value and the actual value of the high-temperature hot water output temperature, n is the number of operations, , and are the proportional adjustment coefficient, the integral adjustment coefficient and the differential adjustment coefficient respectively. Taking the current operating condition requirements as the condition, the required high-temperature hot water output temperature value under the condition is the set value of the system, and the set proportional adjustment parameter, integral adjustment parameter, and differential adjustment parameter are respectively taken as , , .

[0052] Adaptive adjustment of the low-temperature wastewater output temperature: The low-temperature wastewater output temperature (T 19 ) is related to the make-up water temperature of the surplus hot water (T 22 ), the exhaust pressure (P 16 ), the make-up water flow rate of the cooling water (F 12 ), as well as the evaporation temperature, refrigerant phase state, etc. Taking the adjustment of the low-temperature wastewater output temperature of the heat pump system to the set temperature as the only goal, an association model between the low-temperature wastewater output temperature and these variables is established, and the association formula is:

[0053] Taking the rotation speed of the second water pump 12 as the input variable, the low-temperature wastewater output temperature PID controller outputs the set value of the high-temperature hot water output temperature, and adjusts the three parameters of the low-temperature wastewater output temperature PID controller according to the dynamic characteristics of the system , and . After the system goes through one cycle, if there is a difference in the low-temperature wastewater output temperature before and after the cycle, the difference between the two is used as the input parameter and input into the low-temperature wastewater output temperature PID controller. The low-temperature wastewater output temperature PID controller calculates the control amount according to the error of the input parameter and adjusts the rotation speed of the second water pump to change the make-up water flow rate of the surplus hot water. As the parameters of the low-temperature wastewater output temperature PID controller are set reasonably, the calculated result temperature will get closer and closer to the assumed target value until the difference between the two is 0; adjust multiple parameters according to different working conditions, supplemented by the real-time adjustment of the low-temperature wastewater output temperature by the low-temperature wastewater output temperature PID controller, so that the wastewater output by the system can reach the set demand value; The low-temperature wastewater output temperature PID controller calculates by the difference method, and the second water pump 12 dynamically adjusts the rotation speed The calculation formula is:

[0054] wherein, is the difference between the set value and the actual value of the low-temperature waste water output temperature, n is the number of operations, , and are the proportional adjustment coefficient, the integral adjustment coefficient and the differential adjustment coefficient respectively. Based on the requirements of the current operating condition, the required low-temperature waste water output temperature value under the condition is the set value of the system. The set proportional adjustment parameter, integral adjustment parameter and differential adjustment parameter are respectively set to , , .

[0055] In the optimization process of the waste heat source transcritical CO 2 heat pump system, the coupled optimization of the discharge pressure and discharge temperature of compressor 1 is the key to improving the overall performance of the system, and there is a close mutual influence between the two. The increase in discharge pressure usually leads to an increase in discharge temperature, which can improve the system heat recovery efficiency and heating capacity to a certain extent. However, the increase in discharge pressure may also lead to an increase in the compressor load, resulting in an increase in system power consumption. Therefore, the optimization between discharge pressure and discharge temperature must be based on ensuring efficient heat exchange and heat recovery, and avoid adverse consequences such as excessive adjustment causing too high compressor temperature or system overload. The core of the optimization process is to find the best ratio of discharge pressure to discharge temperature through precise control, so as to achieve long-term efficient and stable operation under different working conditions.

[0056] In the coupled optimization process of discharge pressure and discharge temperature in the present invention, an optimization method based on a PID control module is adopted. The PID control module will dynamically adjust the set values of discharge pressure and discharge temperature according to real-time feedback signals, such as discharge pressure, discharge temperature, make-up water temperature of surplus hot water, make-up water temperature of cooling water, load change, etc., to ensure that the system can maintain the best heat pump performance under different working conditions, maximize the coefficient of performance, optimize the heat recovery efficiency, so as to achieve the best energy efficiency output. By adjusting the three parameters , and of the PID control module to adjust the working state of the system in real time to achieve the optimal performance, the optimization correlation formula of discharge pressure and discharge temperature can be described by the following mathematical relationship:

[0057]

[0058]

[0059] Through the PID control algorithm, the exhaust pressure and exhaust temperature can be adjusted in real time during actual operation to meet the optimal working requirements of the heat pump system under different loads.

[0060] In the present invention, the coupled optimization of the exhaust pressure and exhaust temperature is a key factor in improving the system performance. Reasonably adjusting the exhaust pressure and exhaust temperature not only helps to optimize the heating coefficient of the waste heat source transcritical CO 2 heat pump system, improve the heat recovery efficiency, but also effectively reduces energy consumption and extends the service life of the equipment. Therefore, optimizing the coordination of the exhaust pressure and exhaust temperature to ensure the efficient operation of the system under variable working conditions is the core of achieving the best performance of the system. The exhaust pressure and exhaust temperature are closely related in the waste heat source transcritical CO 2 heat pump system, and there is a complex mutual coupling relationship between them. The exhaust pressure has a great impact on the compressor power consumption, the cooling efficiency of the gas cooler and the overall performance of the system. As the exhaust pressure increases, the exhaust temperature usually rises accordingly, which can improve the heat recovery effect of the system, but at the same time increases the load of the compressor. Therefore, the optimization between the exhaust pressure and the exhaust temperature needs to avoid the phenomenon of system overload or too high compressor temperature on the basis of ensuring efficient heat exchange and heating capacity. The core objective of the system optimization method of the present invention is to make the heating coefficient (COP) of the system reach the maximum by adjusting the ratio of the exhaust pressure and exhaust temperature of the compressor 1, optimize the heat recovery efficiency, and avoid system overload and high-temperature operation of the compressor 1. Supplementary with three PID controllers of the intermediate temperature on the water side, the high-temperature hot water output temperature, and the low-temperature waste water output temperature, jointly adjust the system to be able to operate stably in the best state under any working conditions.

[0061] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A waste heat source transcritical CO2 heat pump system, characterized in that: It includes a refrigerant connecting pipeline, a gas cooler water side connecting pipeline, an evaporator water side connecting pipeline and a PID control module; A compressor (1) is provided in the refrigerant connecting pipeline, the outlet of the compressor (1) is connected to the inlet of the first gas cooler (2), the outlet of the first gas cooler (2) is connected to the high-pressure side inlet of the intermediate heat regenerator (4), the high-pressure side outlet of the intermediate heat regenerator (4) is connected to the inlet of the second gas cooler (3), the outlet of the second gas cooler (3) is connected to the electronic expansion valve (5), the electronic expansion valve (5) is connected to the inlet of the evaporator (6), the outlet of the evaporator (6) is connected to the low-pressure side inlet of the intermediate heat regenerator (4), the low-pressure side outlet of the intermediate heat regenerator (4) is connected to the inlet of the compressor (1), and a bypass regulating valve (8) is connected in parallel to the high-pressure side of the intermediate heat regenerator (4); In the gas cooler water side connecting pipeline, the water inlet of the second gas cooler (3) is provided with a first water pump (11), the water outlet of the second gas cooler (3) is connected to the water inlet of the first gas cooler (2), the water outlet of the first gas cooler (2) is connected to a high-temperature hot water use location, and the water side of the second gas cooler (3) is connected in parallel with a water temperature regulating valve (9); In the evaporator water-side connecting pipeline, a second water pump (12) is provided at the water inlet of the evaporator (6), and a water outlet of the evaporator (6) is connected to a low-temperature wastewater storage location; The electronic expansion valve (5), the bypass regulating valve (8), the water temperature regulating valve (9), the first water pump (11) and the second water pump (12) are all connected to a PID control module.

2. A waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: A first temperature sensor (15) and a pressure sensor (16) are provided on the outlet pipeline of the compressor (1).

3. A waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: A fifth temperature sensor (20) is provided on the outlet pipeline of the first gas cooler (2), a second temperature sensor (17) is provided on the water inlet pipeline of the first gas cooler (2), and a third temperature sensor (18) is provided on the water outlet pipeline of the first gas cooler (2).

4. A waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: A sixth temperature sensor (21) and a second solenoid valve (14) are provided on the pipeline between the water inlet of the second gas cooler (3) and the first water pump (11).

5. A waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: A flow meter (10) is installed on the parallel pipeline on the water side of the second gas cooler (3).

6. A waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: A gas-liquid separator (7) is connected between the outlet of the evaporator (6) and the low-pressure side inlet of the intermediate heat regenerator (4).

7. The waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: A seventh temperature sensor (22) and a first solenoid valve (13) are provided on the pipeline between the water inlet of the evaporator (6) and the second water pump (12), and a fourth temperature sensor (19) is provided on the water outlet pipeline of the evaporator (6).

8. The waste heat source transcritical CO2 heat pump system according to claim 1, characterized in that: The PID control module comprises a compressor exhaust pressure PID controller, a compressor exhaust temperature PID controller, a water side intermediate temperature PID controller, a high temperature hot water output temperature PID controller and a low temperature waste water output temperature PID controller, the compressor exhaust pressure PID controller is connected to an electronic expansion valve (5), the compressor exhaust temperature PID controller is connected to a bypass regulating valve (8), the water side intermediate temperature PID controller is connected to a water temperature regulating valve (9), the high temperature hot water output temperature PID controller is connected to a first water pump (11), and the low temperature waste water output temperature PID controller is connected to a second water pump (12).

9. An optimization method for a waste heat source transcritical CO2 heat pump system according to any one of claims 1 to 8, characterized in that: include: When the waste heat source transcritical CO2 heat pump system is in operation, the opening of the electronic expansion valve (5) is adjusted by the PID control module so that the exhaust pressure of the compressor (1) reaches an optimal value; the opening of the bypass regulating valve (8) is adjusted by the PID control module so that the exhaust temperature of the compressor (1) and the heat recovery rate of the intermediate heat regenerator (4) reach optimal values; the opening of the water temperature regulating valve (9) is adjusted by the PID control module so that the intermediate temperature on the water side reaches a set value; the rotation speed of the first water pump (11) is adjusted by the PID control module so that the high-temperature hot water output temperature reaches a set value; and the rotation speed of the second water pump (12) is adjusted by the PID control module so that the low-temperature waste water output temperature reaches a set value.

10. The optimization method of the waste heat source transcritical CO2 heat pump system according to claim 9, characterized in that: The optimization process of the exhaust pressure of the compressor (1) is as follows: the compressor exhaust pressure PID controller adjusts the refrigerant flow of the opening control system of the electronic expansion valve (5) according to the exhaust pressure setting value and the actual exhaust pressure value of the compressor (1), so that the exhaust pressure of the compressor (1) reaches the optimal value; The optimization process of the exhaust temperature of the compressor (1) and the system heat recovery rate is as follows: the compressor exhaust temperature PID controller adjusts the opening of the bypass regulating valve (8) according to the exhaust temperature set value and the actual exhaust temperature value of the compressor (1) to control the refrigerant flow of the intermediate heat regenerator (4), so that the exhaust temperature of the compressor (1) and the heat recovery rate of the intermediate heat regenerator (4) reach optimal values; The optimization process of the water side intermediate temperature is as follows: the water side intermediate temperature PID controller adjusts the opening of the water temperature regulating valve (9) according to the water side intermediate temperature of the first gas cooler (2) and the second gas cooler (3) and the refrigerant side intermediate temperature, and changes the water side intermediate temperature value so that the water side intermediate temperature of the first gas cooler (2) and the second gas cooler (3) reaches a set value; The optimization process of the high-temperature hot water output temperature is as follows: the high-temperature hot water output temperature PID controller adjusts the rotation speed of the first water pump (11) and changes the flow rate of cooling water replenishment according to the high-temperature hot water output temperature setting value and the actual value of the water temperature at the water outlet of the first gas cooler (2), so that the water temperature at the water outlet of the first gas cooler (2) reaches the setting value; The optimization process of the low-temperature wastewater output temperature is as follows: the low-temperature wastewater output temperature PID controller adjusts the rotation speed of the second water pump (12) according to the set value of the outlet water temperature of the waste heat and waste water after heat exchange and the actual value of the water temperature at the outlet of the evaporator (6), and changes the flow rate of the waste heat water replenishment on the water channel side of the evaporator (6) so that the water temperature at the outlet of the evaporator (6) reaches the set value.

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